Interactions of Cadmium, Zinc, and Phosphorus in Marine Synechococcus: Field Uptake, Physiological and Proteomic Studies

Alysia Cox, Ph.D., 2011
Mak Saito, Advisor

Enriched stable isotope field uptake studies of ¹¹⁰Cd in the Costa Rica Upwelling dome showed that Cd uptake occurs in waters shallower than 40 m, correlates with chlorophyll a concentrations and is roughly equivalent to the calculated Cd upwelling flux inside the dome. In laboratory experiments, coastal Synechococcus WH5701 exposed to low picomolar quantities of free Cd under Zn deficiency show similar growth rates to no added Cd treatments during exponential growth phase, but show differences in relative abundances of many carbon and sulfur metabolism proteins suggesting great metabolic impact.  During stationary phase, chronic Cd exposure causes an increase in relative chlorophyll a fluorescence and faster mortality rates.  The interactions of acute low picomolar Cd exposure with Zn and phosphate (PO₄^3-) were investigated in open ocean Synechococcus WH8102.  Zn appears vital to the PO₄^3- response of this organism. Comparison with literature transcriptome analyses of PO₄stress shows similar relative abundance increases of PO4^3- stress response proteins including a PO₄^3- binding protein and a Zn-requiring alkaline phosphatase.  A bacterial metallothionein, a Zn-associated protein, appears correlated with proteins present under low PO₄^3-. Together, these experiments suggest that the interactions of Cd and Zn can affect Synechococcus and play a role PO₄^3- acquisition.